AKA Lacto, AKA Mr Kettle Sour, AKA The Tart Maker, is also known as a probiotic.

Produces lactic acid

Trives between 38C and 49C

Most strains are very hop sensitive

Pedioccoccus

AKA Pedio, AKA The Fear Bringer, AKA The Sour Maker

Produces lactic acid, but over long time periods can dramatically lower pH

more hop and acid tolerant than lacto, can drop pH below 3.0

Acetobacter

AKA The Vinegar Maker

Consumes ethanol to produce acetic acid

Ideally kept to a minimum

As with a lot of things in beer, sour generally falls into 2 categories:

Traditional

American Style

1. Traditional

The BJCP gathers traditional sours into category 23 in the 2015 style guide.

23A. Berliner Weisse

23B. Flanders Red Ale

23C. Oud Bruin

23D. Lambic

23E. Gueuze

23F. Fruit Lambic

As well as a couple in the Historical (27) category, Gose and Lichtenhainer.

Production

Traditional Sours are produced in many different ways, so this section is only an overview of how one can be produced.

Traditional Belgian sours are generally inoculated by allowing them to cool in large vessels called coolships and having wild yeast enter the beer; spontaneous fermentation.

A coolship (Anglicized version of the Dutch/Flemish koelschip) is a type of fermentation vessel used in the production of beer. Traditionally, a coolship is a broad, open-top, flat vessel in which wort cools. The high surface to mass ratio allows for more efficient cooling. Wikipedia

Cantillon coolship

Homebrew coolship

The beer is then aged, generally in wood, possibly fruited or dry hopped, and blended before bottling.

American Style

The BJCP gathers American Wild into category 28 in the 2015 style guide.

28A. Brett Beer

28B. Mixed-Fermentation Sour Beer

28C. Wild Specialty Beer

Not all these beers have to be, or are sour

Most often drier and fruitier than the base style suggests. Funky notes range from low to high, depending on the age of the beer and strain(s) of Brett used. Funkiness is generally restrained in younger 100% Brett examples but tends to increase with age. May possess a light acidity, although this does not come from Brett. BJCP Guidelines 28A Brett Beer.

A sour and/or funky version of a fruit, herb, or spice beer, or a wild beer aged in wood. If wood-aged, the wood should not be the primary or dominant character. BJCP Guidelines 28C. Wild Specialty Beer

All three styles require a base style to be declared when entering them, and so are very open categories. This gives brewers the ability to really experiment and think outside of the box. Commercial examples can range from very light like Jester King’s Le Petit Prince

Category: Stainless Steel Fermented

ABV: 2.9% FG: 1.000 IBU: 37

Water: Hill Country Well Water

Grains: Two-Row Malt, Wheat Malt

Hops: Perle, Fuggles, Czech Saaz

Fermentation: Farmhouse Yeast, Native Yeast and Souring Bacteria from the Texas Hill Country

Quick Sour at Home

Souring in the Boil Kettle aka Kettle Sour.

A pH meter is strongly recommended if you want to kettle sour.

A kettle sour is not much different than a regular brew day. The big difference is that once you have collected your wort into your kettle (optionally boiling briefly first), you pitch lactobacillus and allow it to sour the wort for a period of time (1-4 days) and then proceed with your brew day.

Benefits of Kettle Souring for Homebrewers

Breaks the brew day into 2

Day 1, Mash and lauter, pitch lactobacillus.

Day 2, Boil, cool, begin fermentation

Doesn’t require separate equipment for souring as no bacteria come in contact with your equipment

Quick results mean more beer faster

Drawbacks of Kettle Souring for Homebrewers

Kettle sours tend to lack the character of longer aged sours

Space to keep the warm kettle for 1-5 days while it sours

Adds another step to the brew day

Technique:

After lautering pasteurise the wort to prevent infection from grain. 1-2 minute boil is ideal.

Cool to desired temperature (likely around ~40C)

Drop pH under 4.5 (4.0-4.3) using lactic acid

Pitch lactobacillus. This can be a pitch from a yeast producer, or some yoghurt or probiotics

Purge the head space of your kettle with CO2 to decrease off-flavors such as “footiness”

Hold at desired temperature (based on the strain of lactobacillus you are using, likely around ~40C)